Terminal oxidases bacterial

Cytochrome oxidase (cytochrome aa3) represents the most important cytochrome of the a class. This is the terminal oxidase used in animals, plants, yeasts, algae and some bacteria. It contains two copper centres, giving four redox groups in total. This oxidase is discussed with other cytochromes that have a terminal oxidase function in Sections 62.1.12.4 and 62.1.12.5. These are cytochromes o, d and cd,. The oxidases fed719 and ax are not included in that discussion. The situation regarding cytochrome ax has been confused, partly due to uncertainty in the definition of this cytochrome. In some respects, the properties of cytochrome ax resemble those of mitochondrial and bacterial aa3. It functions as a terminal oxidase in some bacteria,720 but its role in E. coli is unknown. A soluble fraction from disrupted E. coli cells grown anaerobically on glycerol and fumarate contains a hemoprotein similar to cytochrome ax, which has catalase and peroxidase activity.721... 

The redox partners of these proteins have yet to be identified, although it has been shown that auracyanins can donate electrons to the membrane-bound cytochrome c-554, which is the direct electron donor for the photooxidized bacterial reaction center P870+ (McManus et al., 1992). However, whether it is their proper in vivo function remains uncertain. The sulfocyanin gene is in the same operon with the components of the respiratory electron transfer chain and, since Su. acidocaladar-ius completely lack c-type cytochromes, it is implicated as a substrate for the CuA-containing terminal oxidase. Interestingly, the occurrence of... 

A wide variety of different cytochrome-linked electron-transfer systems is encountered in bacteria respiratory chains with oxygen, nitrate or sulphate as electron acceptors, fumarate reductase systems and light-driven cyclic electron-transfer systems (Fig. 3). All these systems are composed of several electron-transfer carriers, the nature of which varies considerably in different organisms. Electron carriers which are most common in bacterial electron-transfer systems are flavoproteins (dehydrogenases), quinones, non-heme iron centres, cytochromes and terminal oxidases and reductases. One common feature of all electron-transfer systems is that they are tightly incorporated in the cytoplasmic membrane. Another important general property of these systems is that electron transfer results in the translocation of protons from the cytoplasm into the external medium. Electron transfer therefore... 

Sotiriou C, Chang CKJ (1988) Synthesis of the Heme Prosthetic Group of Bacterial Terminal Oxidase. J Am Chem Soc 110 2264... 

Nitrite reductases and nitrous oxide reductases are relatively newly found copper-containing proteins involved in bacterial denitrification. N2O reductase may bear a relationship to cytochrome oxidase and, indeed, parallels it somewhat in function, being the terminal electron acceptor in its pathway. 

Poole1305 has reviewed the bacterial cytochrome oxidases, and has drawn attention to features which are not present in the mitochondrial enzyme, and which reflect the metabolic diversity and adaptability of bacteria. These are (1) the synthesis of the oxidases is controlled dramatically by the prevailing environmental conditions (2) some oxidases are multifunctional, and may use electron acceptors other than dioxygen (3) more than one type of oxidase may be present, each terminating a branched electron-transfer pathway. 

Many key protein ET proeesses have become accessible to theoretical analysis recently because of high-resolution x-ray structmal data. These proteins include the bacterial photosynthetic reaction centre [18], nitrogenase (responsible for nitrogen fixation), and eytoehrome c oxidase (the terminal ET protein in mammals) [19. 20]. Although much is understood about ET in these molecular machines, considerable debate persists about details of the molecular transformations. 

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